Securities with Unrealized Losses (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Temporarily Impaired Securities
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	$ 79		$ 285
Less than twelve months, Unrealized Losses	0		0
Twelve months or longer, Fair Value	37		40
Twelve months or longer, Unrealized Losses	8		9
Total, Fair Value	116		325
Total, Unrealized Losses	8		9
Temporarily Impaired Securities | US Government Agencies Debt Securities
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	30		10
Less than twelve months, Unrealized Losses	0		0
Twelve months or longer, Fair Value	0		0
Twelve months or longer, Unrealized Losses	0		0
Total, Fair Value	30		10
Total, Unrealized Losses	0		0
Temporarily Impaired Securities | US States and Political Subdivisions Debt Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	0		1
Less than twelve months, Unrealized Losses	0		0
Twelve months or longer, Fair Value	25		28
Twelve months or longer, Unrealized Losses	6		4
Total, Fair Value	25		29
Total, Unrealized Losses	6		4
Temporarily Impaired Securities | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	49		224
Less than twelve months, Unrealized Losses	0		0
Twelve months or longer, Fair Value	0		1
Twelve months or longer, Unrealized Losses	0		0
Total, Fair Value	49		225
Total, Unrealized Losses	0		0
Temporarily Impaired Securities | Collateralized Debt Obligations [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value			50
Less than twelve months, Unrealized Losses			0
Twelve months or longer, Fair Value			0
Twelve months or longer, Unrealized Losses			0
Total, Fair Value			50
Total, Unrealized Losses			0
Temporarily Impaired Securities | Asset-backed Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	0		0
Less than twelve months, Unrealized Losses	0		0
Twelve months or longer, Fair Value	12		11
Twelve months or longer, Unrealized Losses	2		5
Total, Fair Value	12		11
Total, Unrealized Losses	2		5
Other Than Temporarily Impaired Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	0	[1]	16	[1]
Less than twelve months, Unrealized Losses	0	[1]	1	[1]
Twelve months or longer, Fair Value	50	[1]	209	[1]
Twelve months or longer, Unrealized Losses	2	[1]	32	[1]
Total, Fair Value	50	[1]	225	[1]
Total, Unrealized Losses	2	[1]	33	[1]
Other Than Temporarily Impaired Securities [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	0	[1]	15	[1]
Less than twelve months, Unrealized Losses	0	[1]	1	[1]
Twelve months or longer, Fair Value	46	[1]	206	[1]
Twelve months or longer, Unrealized Losses	0	[1]	30	[1]
Total, Fair Value	46	[1]	221	[1]
Total, Unrealized Losses	0	[1]	31	[1]
Other Than Temporarily Impaired Securities [Member] | Asset-backed Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	0	[1]	1	[1]
Less than twelve months, Unrealized Losses	0	[1]	0	[1]
Twelve months or longer, Fair Value	4	[1]	3	[1]
Twelve months or longer, Unrealized Losses	2	[1]	2	[1]
Total, Fair Value	4	[1]	4	[1]
Total, Unrealized Losses	2	[1]	2	[1]
Impaired Securities
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	79		301
Less than twelve months, Unrealized Losses	0		1
Twelve months or longer, Fair Value	87		249
Twelve months or longer, Unrealized Losses	10		41
Total, Fair Value	166		550
Total, Unrealized Losses	$ 10		$ 42

[1] Includes OTTI securities for which credit losses have been recorded in earnings in current or prior periods.